Custom Search
|
|
|
||
 1.5 Underground Conduit System. I n s u l a t i o n for underground systems should
conform to the DOD adopted ASTM C-552, Specification for Cellular Glass Block
a n d Pipe Thermal Insulation. Pipe insulation should be a nonconductor of
e l e c t r i c i t y , v e r m i n p r o o f , r o t resistant, and noncorrosive to the pipe when
wet. A l l p i p i n g , f l a n g e s , v a l v e s , f i e l d j o i n t s , a n d f i t t i n g s s h o u l d b e
i n s u l a t e d with the same material and equal thickness as the insulation of the
a d j o i n i n g pipe. A continuous annular space (l-inch minimum) is commonly
p r o v i d e d between the outer surface of premolded or preformed pipe insulation
a n d the inner surface of the exterior casing. T h i s provides an adequate air
p a s s a g e for venting and draining.
1 . 6 Exposed Piping. A l l e x t e r i o r p i p e s , v a l v e s , f l a n g e s , a n d f i t t i n g s
exposed in manholes or exposed aboveground should be covered with insulation.
T h e insulation should be waterproofed and covered for protection with an
aluminum jacket.
1 . 7 I n s t a l l a t i o n . I n s u l a t i o n should be installed in such a manner that it
w i l l not be damaged by pipe expansion or contraction. Metal bands or straps
u s e d to hold insulation in place should be of stainless steel. Wire should
n o t be used for this purpose. W i t h prefabricated casings containing molded or
p r e f o r m e d insulation already in place around the piping, special installation
procedures may be required and precautions must be taken to ensure the
i n s u l a t i o n is kept absolutely dry.
1 . 8 Maintenance. Maintenance of insulation includes prompt repair of damaged
s u r f a c e s , repainting and waterproofing, tightening bands, and repairing
p r o t e c t i v e covering. M a k e certain that fluid temperatures do not rise above
t h e safe limit for the material used. Unnecessary and expensive heat losses
w i l l occur if insulation removed for repairs is not promptly replaced.
2 FREEZE PROTECTION. When the heat distribution system is to be shut down
f o r a significant period of time during freezing weather, all steam lines,
condensate lines, high temperature water (HTW) lines, and compressed air lines
and equipment should be protected from freezing by completely draining the
system. O c c a s i o n a l l y , installations are provided with tracing systems to
p r e v e n t freezing during shutdowns of short duration. In those cases, the
s y s t e m need not be drained, as the tracing system will maintain the water
t e m p e r a t u r e above the freezing point (32F).
3 TRACING.
E i t h e r steam or electrical tracing systems are available.
3 . 1 Steam Tracing. Where a source of low- or medium-pressure steam is
a v a i l a b l e , small diameter steam lines, called steam tracers, are installed
b e s i d e the pipelines to maintain the water temperature above the freezing
p o i n t during short duration shutdowns. T h e tracing lines are provided with
t r a p s for condensate drainage. T h e condensate can be either reinfected into
the condensate return system or disposed of, depending on economic
considerations.
3 . 2 E l e c t r i c T r a c i n g . Where an adequate source of steam is not available, or
e c o n o m i c considerations dictate its use, electric tracing is employed.
T r a c i n g is provided by flexible electric heating cables wrapped around the
p i p e l i n e s , v a l v e s , a n d f i t t i n g s . E l e c t r i c tracing cable normally consists of
twin resistor wires accurately positioned in high dielectric refractory
7-4
|
 
|
|
|
||
